1. Field of the Invention
The present invention relates to a local timer which is used in a wireless LAN(Local Area Network).
2. Description of the Related Art
A wireless LAN(Local Area Network) system uses an IEEE 802.11 standard. In an infrastructure mode, a beacon signal is transmitted from an access point. The beacon signal is received in a station. A copy of a TSF(Timing Synchronization Function) timer value is managed in the station based on a time stump field of the beacon signal frame. If the beacon signal is not received normally, the station can achieve a clock synchronization by referring the TSF timer value in the station.
In such a station, a 40-Mhz high-speed clock is generated and supplied to a base band LSI as a reference clock. The station has a power saving mode. In the power saving mode, a power consumption is reduced by suspending the supply of the high-speed clock.
While the high-speed clock is suspended, a suspending time is measured by another low-speed clock. Therefore, the wireless LAN station can reduce power consumption. Such technique is described in Japanese Patent Laid-Open 2003-318771.
In the wireless LAN station which is described above, the TSF timer value which is operated in the high-speed clock should continuously be the same as the TSF time value which is operated in the high-speed clock with interval.
For achieving this operation, a suspending time of the high-speed clock is synchronized with the low-speed clock, and then, the TSF timer value which is operated after restarting is set to the TSF timer.
However, if the suspending time of the high-speed clock is synchronized with the low-speed clock, the high-speed clock is continued untill the next timing of the low-speed clock arrives. Therefore, it is difficult to reduce power consumption. Also, if the TSF timer value which is operated after restarting is set to the TSF timer, the TSF timer value which is set in the TSF timer may not be accurate.